System and Method for Controlling Hydraulic Fluid Flow

ABSTRACT

A system and method for controlling fluid flow through a hydraulic valve in a work machine is disclosed. The system and method may include receiving an input command by a controller configured to control a fluid flow to an actuator, the input command generated by an input controller. The system and method may also include receiving a parameter indicative of pump flow by the controller, determining a first valve command corresponding to the input command and determining a second valve command based upon the parameter that achieves the fluid flow to the actuator corresponding to the first valve command.

TECHNICAL FIELD

The present disclosure generally relates to hydraulic valves and, more particularly, relates to a system and method for controlling fluid flow through hydraulic valves in response to available pump flow.

BACKGROUND

A variety of work machines such as, loaders, excavators, motor graders, and other types of construction, work and earth moving machinery use one or more hydraulically actuatable implements for accomplishing a task. These hydraulically actuatable implements may be operated by a hydraulic actuator, such as, a cylinder and a piston assembly. The cylinder may be in fluid communication with a hydraulic pump for providing pressurized fluid to the chambers thereof, as well as in fluid communication with a fluid source or a tank for draining pressurized fluid therefrom. A valve arrangement may be connected between the pump and the cylinder and/or between the cylinder and the fluid source to control the flow rate and direction of pressurized fluid to and from the chambers of the cylinder.

The valve arrangement may include one or more electrically actuated valves that may be controlled to vary the amount of pressurized fluid flowing between the pump and the fluid source via the cylinder. The amount of the pressurized fluid flowing to/from the cylinder may be controlled by changing the displacement of a valve spool present in each valve. Changing the displacement of the valve spool, which may be accomplished by using an electrically controlled solenoid wound around an armature, may change an opening area of one or more orifices present within the valve through which the fluid may flow through. When current is applied to the solenoid, the armature may move under electro-magnetic forces generated by the solenoid to cause the associated valve spool to displace a certain amount. For precise flow control, the valve spool (and therefore the orifices) needs to be controlled accurately.

The displacement of the valve spool can be changed by an input command issued by an operator. Each input command may correspond to a pre-determined amount of valve spool displacement and, therefore, a pre-determined fluid flow through the hydraulic valve. The rate of flow through the hydraulic valve may be dependent upon pump flow (that is, available fluid flow from the pump). As the pump flow varies, the fluid flow through the hydraulic valve may vary. Thus, for the same input command, changes in pump flow may vary the fluid flow through the hydraulic valve to an actuator.

Therefore, the performance of an implement hydraulically controlled by an input command may vary depending upon the pump flow. For example, for a given input command, an implement may operate at one velocity for one pump flow and the implement may operate at another velocity for another pump flow. This not only affects the time taken to accomplish a task, it also affects the productivity of the operator who has to continuously account for the variations in pump flow when issuing input commands to achieve a consistent performance from the implement.

One way of controlling the fluid flow through a hydraulic valve is disclosed in U.S. Pat. No. 7,814,749. Here, the flow rate through the hydraulic valve is varied in response to an operator command signal and a throttle position signal. Thus, the '749 patent controls the hydraulic system based upon a throttle position, not pump flow. Specifically, this prior art patent looks at available flow relative to commanded flow and only takes action if the commanded flow is greater than available flow. Furthermore, the prior art patent is designed for post-compensated valves, which by design control flow rates based upon commanded flow versus available flow.

It would accordingly be beneficial if a mechanism to control the fluid flow through a hydraulic valve irrespective of pump flow is developed. It would additionally be beneficial if the mechanism could control fluid flow irrespective of commanded and available flows, as well as be designed for non-compensated valves.

SUMMARY

In accordance with one aspect of the present disclosure, a method of controlling fluid flow in a work machine is disclosed. The method may include receiving an input command by a controller configured to control a fluid flow, the input command generated by an input controller. The method may also include receiving a parameter indicative of pump flow by the controller, determining a first valve command corresponding to the input command and determining a second valve command based upon the parameter that achieves the fluid flow to an actuator corresponding to the first valve command.

In accordance with another aspect of the present disclosure, a system for controlling fluid flow through a hydraulic valve in a work machine is disclosed. The system may include an input controller to generate an input command, a parameter determinator to determine a pump flow of the work machine and a controller configured to receive the input command and the pump flow. The controller may be further configured to determine a first valve command corresponding to the input command and a second valve command based upon the pump flow that achieves the fluid flow to an actuator corresponding to the first valve command.

In accordance with yet another aspect of the present disclosure, a work machine is disclosed. The work machine may include an engine, an input controller for generating a plurality of input commands and a pump flow sensor for determining a pump flow. The work machine may also include a controller in at least indirect communication with the input controller and the pump flow sensor, the controller configured to determine a first valve command corresponding to the plurality of input commands, the controller also configured to determine a second valve command that achieves a fluid flow to an actuator corresponding to the first valve command when variations in the pump flow occur, the first and the second valve commands used to control the fluid flow to the actuator through a hydraulic valve.

These and other aspects and features of the present disclosure will be more readily understood upon reading the following description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary work machine constructed in accordance with at least some embodiments of the present disclosure;

FIG. 2 is a schematic illustration of a control system utilized to control the flow of hydraulic fluid within the work machine of FIG. 1 in response to variations in pump flow, in accordance with at least some embodiments of the present disclosure;

FIG. 3 is a flowchart outlining exemplary steps that the control system of FIG. 2 may follow in controlling the hydraulic fluid flow; and

FIG. 4 is a graphical illustration representing an exemplary relationship between an input controller movement and hydraulic fluid flow in response to the variations in pump flow.

While the present disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof, will be shown and described below in detail. It should be understood, however, that there is no intention to be limited to the specific embodiments disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents along within the spirit and scope of the present disclosure.

DETAILED DESCRIPTION

The present disclosure teaches, among other things, a system and method for controlling fluid flow through a hydraulic valve in a work machine. The fluid flow may be controlled by a controller such that for a given input command, the fluid flow through the hydraulic valve to a hydraulic cylinder remains constant irrespective of the variations in pump flow.

Referring now to FIG. 1, an exemplary work machine 2 is shown, in accordance with at least some embodiments of the present disclosure. While the work machine 2 has been shown to be a track type tractor, it will be understood that in other embodiments, the work machine may be a wheel loader, skid-steer loader, a backhoe-loader, other type of small, medium or large track or wheel type tractor or loader, a harvester, a paving machine, or any other type of work, construction, agricultural or earth moving machine that utilizes a hydraulically actuatable implement or component for accomplishing a task.

The work machine 2 may include an engine frame 4 connected at least indirectly to an operator station 6. Tracks 8 or other ground engaging mechanism (such as wheels) may be employed for navigating the work machine 2. The engine frame 4 may house a power source, such as an engine 10 and other power train components (such as a transmission, not shown) for generating and delivering power to operate the work machine 2. The engine may be a gasoline, diesel, or any other type of engine that is commonly employed with such work machines. The work machine 2 may even draw power from other power sources, such as natural gas, fuel cells, etc. The engine frame 4 may also house a hydraulic system for hydraulically actuating an implement system 14.

The implement system 14 may include a work implement, such as a blade 16. The blade 16 may be configured for secure attachment to the work machine 2, and for release and substitution of another implement when desired. The blade 16 may be connected for operation to the engine frame 4 by a mount 18. The operation of the mount 18 may be controlled by one or more actuators, such as, hydraulic cylinders. The hydraulic cylinders may be extended or retracted to operate the mount 18. The operation of the hydraulic cylinders may in turn be controlled by the hydraulic system under command by an operator operating the work machine 2.

With respect to the operator station 6, although not visible in the figures, it may include a plurality of operator controls and operator interfaces for controlling the operation of the work machine 2 and the various work implements 16 connected thereto, as well as for navigating and steering the work machine 2 on a work surface. For instance, the operator station 6 may house various hand controlled operator interfaces, such as, joystick controls, pedals, buttons, instrument panels, gauges and warning lamps for keeping the operator aware of any critical system information, as well as safety and convenience features such as cup holders, lighters, etc. In at least some embodiments, the operator station 6 may also house at least a portion of a control system 20 (See FIG. 2), described in greater detail below. Other devices and components that commonly exist in such machines may be present in the operator station 6 of the work machine 2.

Notwithstanding the components of the work machine 2 described above, it will be understood that several other components of the work machine 2, as well as components that may be employed in combination or conjunction with the work machine are contemplated and considered within the scope of the present disclosure.

Turning now to FIG. 2, the control system 20 is shown and described in accordance with at least some embodiments of the present disclosure. As shown, the control system 20 may include a controller 22 capable of at least indirectly receiving information from a pump flow sensor 24 and an input controller 26. The controller 22 may be a stand-alone or networked embedded or general purpose processing system having any of a variety of volatile or non-volatile memory/storage devices, such as, flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), etc., processing devices, such as, microprocessors and central processing units, and computer readable media, such as, joysticks, flash drives, optical disc drives, floppy discs, magnetic tapes, drums, cards, etc. The controller 22 may also include output and display devices such as monitors and printers. Other types of computing, processing as well as reporting and storage devices may be present within (or used in conjunction with) the controller 22. The controller 22 may run one or more software programs or applications stored in a memory location, read from a computer readable medium, and/or accessed from an external device operatively coupled to the controller by any suitable communication network.

While in at least some embodiments, the controller 22 may be housed within the operator station 6, this need not always be the case. In other embodiments, the controller 22 or portions thereof may be housed elsewhere on the work machine 2. Furthermore, the controller 22 may communicate with the pump flow sensor 24 and the input controller 26 via communication links 28 and 30, respectively. One or both of the communication links 28 and 30 may be wired or wireless communication links including, radio channels and links involving the internet or the World Wide Web (WWW). Other types of communication links (such as mechanical links) that are employed in work machines 2 may also be used for the communication links 28 and 30. As discussed above, using the communication link 28, the controller 22 may receive information from the pump flow sensor 24. The pump flow sensor 24 may be configured to read or sense the available fluid flow from a pump 38 via a communication link 32 and transmit the sensed flow to the controller 22 via the communication link 28.

Any of a variety of pump flow sensors, pump speed sensors or any sensors indicative of pump flow that are commonly used in work machines may be used for purposes of this disclosure. In at least some embodiments, a cylinder displacement sensor may be utilized for monitoring closed loop velocity, which in turn may be indicative of pump flow. In yet other embodiments, an engine speed sensor may be used to determine the engine speed and the engine speed may be used to determine pump flow (since as the engine speed varies, the pump flow varies). Similarly, it will be understood that other parameters that may be used either directly or indirectly to determine pump flow are contemplated and considered within the scope of the present disclosure. Furthermore, the communication link 32 may be similar to the communication links 28 and 30 described above.

Relatedly, the controller 22 may receive information (e.g., commands) from the input controller 26. The input controller 26 may be any of a variety of input devices, some of which, such as joysticks, are described above and may be utilized by an operator to issue commands for controlling various aspects of the work machine 2. The input controller 26 may be located within the operator station 6, elsewhere on the work machine 2, or even remotely in the case of a remote controlled vehicle. By virtue of operating the input controller 26, an input command identifying the operation (e.g., movement of the implement system 14) may be sent to the controller 22 via the communication link 30. The input controller 26 may, in at least some embodiments, also include interfaces with electronic control such as, global positioning systems (GPS) and laser guided systems to communicate with the controller 22.

Utilizing the input command from the input controller 26 and pump flow from the pump flow sensor 24, the controller 22 may control a hydraulic valve 34 via communication link 36. It will be understood that for purposes of explanation, only one hydraulic valve 34 has been shown in the present disclosure. Typically, however, several hydraulic valves, controlling various aspects of the work machine 2 may be present and, some or all of those hydraulic valves may be controlled by the controller 22 in response to variations in pump flow.

With respect to the hydraulic valve 34, in at least some embodiments, it may be a non-compensated valve configured to communicate fluid between the pump 38, a tank 40 and a hydraulically powered device 42, such as, a hydraulic cylinder or hydraulic motor. Furthermore, in at least some embodiments, the hydraulic valve 34 may be a supply valve or a drain valve. Other types of hydraulic valves that are commonly used in work machines may also be used for purposes of this disclosure. As shown, the hydraulic valve 34 may include a valve spool 44 and an actuator 46 to control the flow of hydraulic fluid (e.g., flow rate) therethrough. The actuator 46 may include an armature having a solenoid wound therearound and, thus, may be electrically controlled. In other embodiments, other types of actuators may be employed as well.

The controller 22 may apply a current signal to the solenoid for actuating the actuator 46, which in turn may displace the valve spool 44. Displacing the valve spool 44 may vary the opening area of one or more orifices 48, 50 and 52 to vary the hydraulic fluid flow through the hydraulic valve 34. Notwithstanding the fact that in the present embodiment, the hydraulic valve 34 has been shown with three of the orifices 48-52, in at least some embodiments, the number of orifices may vary. The pump 38 may supply pressurized hydraulic fluid from the tank 40 to the hydraulically powered device 42 through the hydraulic valve 34. Pressurized hydraulic fluid may also flow from the hydraulically powered device 42 back to the tank 40.

In at least some embodiments and, as shown, the pump 38 may be a fixed displacement pump, although other types of pumps (e.g., variable displacement pumps) that are commonly employed in hydraulic systems may be employed as well. Relatedly, the tank 40 may be a reservoir or other type of fluid source that may be capable of storing a supply of fluid, such as, hydraulic fluid, lubrication oil, transmission oil or other types of machines oils and fluids utilized within the work machine 2. The operation of a hydraulic valve is well known in the art and, therefore, has not been described here in greater detail.

Referring still to FIG. 2 and as discussed above, the rate at which hydraulic fluid is pumped through the pump 38 (pump flow) may vary with the speed of the engine 10. In other words, the speed of the engine 10 may affect the pump speed and the pump flow. This is represented by communication link 54, which in at least some embodiments may be a mechanical link typically employed in the work machine 2. By virtue of increasing or decreasing the speed of the pump 38 (by increasing or decreasing the speed of the engine 10), the flow of hydraulic fluid through the orifices 48-50 of the hydraulic valve 34 may vary for a given signal to the actuator 46, which in turn may vary the performance and response of the hydraulically powered device 42.

As will be discussed further below with respect to FIGS. 3 and 4, the controller 22 may be utilized to ensure a constant rate of hydraulic fluid flow through one or more of the orifices 48-52 of the hydraulic valve 34 for a given input command irrespective of pump flow, thereby ensuring a consistent performance and response from the hydraulically powered devices 42. For example, in at least some embodiments, the controller 22 may ensure a constant fluid flow through the orifice 48 to the actuator 42, and as the pump flow decreases (or increases), the controller may reduce (or increase) flow through the orifice 50 and vice-versa.

Notwithstanding the components of the control system 20 described above, it will be understood that several other components and/or systems that are commonly used within the control systems of work machines may be employed. For example, the control system 20 may include various other types of sensors for reading and/or sensing other parameters within the work machine 2, other hydraulic pumps and fluid sources, pressure compensator devices, etc.

INDUSTRIAL APPLICABILITY

In general, the present disclosure has industrial applicability in connection with a wide range of machines used in agricultural, construction and earth moving operations. More specifically, the disclosure sets forth a system for controlling hydraulic fluid flow in such machines. The control system is configured to receive input commands from an input controller, as well as pump flow from a pump flow sensor. The control system controls the fluid flow through a hydraulic valve for a given input command irrespective of pump flow. In doing so, performance and response time of hydraulically controlled devices of the above mentioned machines is improved.

Referring now to FIG. 3, a flowchart 56 outlining the steps in controlling the fluid flow through the hydraulic valve 34 for a given input command as the flow from the pump 38 increases or decreases is shown, in accordance with at least some embodiments of the present disclosure. After starting at a step 58, the process proceeds to a step 60. At the step 60, the controller 22 receives an input command from the input controller 26 via the communication link 30. As discussed above, the input command may be issued by an operator operating the work machine 2 in response to some action desired by a component or system of the work machine. For example, an operator may issue an input command when operation of a hydraulically actuated implement system (e.g., the hydraulically powered device 42) is desired. While in the present embodiment, the input command is issued by an operator, in at least some embodiments, the input command may be issued by another computer control system, such as, the Accugrade™ control system manufactured by the assignee of the present application.

The input command may be related to the signal to the actuator 46 and the rate of fluid flow through the hydraulic valve 34 via a predefined relationship that may be pre-set within the controller 22. For example, the controller 22 may include a look-up table or database that may identify the rate of fluid flow for each input command. In at least some embodiments, the rate of fluid flow may be identified by the percentage of total available opening area of the orifices 48-52. The greater the opening of the orifices 48-52, the greater the amount of fluid flowing therethrough and, thus, the greater the rate of fluid flow. In at least some embodiments, the fluid flow may also be determined by measuring the actual velocity of a hydraulically controlled component.

Next, at a step 62, the controller 22 may receive pump flow from the pump flow sensor 24. The pump flow sensor 24 may transmit the current pump flow to the controller 22 via the communication link 28. As discussed above, the pump flow may vary depending upon a variety of engine parameters, such as, engine speed. Thus, while for a given input command from the input controller 26, the orifices 48-52 of the hydraulic valve 34 may be designed to open (or close) by a pre-set percentage, the fluid flow may increase or decrease as the pump flow (or engine speed, for example) increases or decreases for the same input command. By virtue of utilizing the control system 20 discussed above, the fluid flow through the hydraulic valve 34 may be maintained at the pre-set percentage for a given input command irrespective of the pump flow.

Specifically, at a step 64, the controller 22 may determine the necessary adjustment to the opening area of the orifices 48-52 and particularly, to the orifices 48 and 50 of the hydraulic valve 34, that may be needed to account for the variation in the pump flow. Accordingly, the controller 22 may first determine (e.g., from a look-up table) the fluid flow through the hydraulic valve 34 for the input command received at the step 60. In addition to the input command-fluid flow relationship pre-set within the controller 22, the controller may also have pre-set therein another look-up table or database that defines a relationship between pump flow and adjustment of orifice size needed for a given input command to maintain the rate of fluid flow for that input command. The controller 22 may also utilize a closed loop control based on speeds of the hydraulic cylinder 42 to determine the valve commands. Thus, the controller 22 may refer to the look-up table for the current pump flow received at the step 62 and determine the amount of adjustment needed to the orifice size of the hydraulic valve 34. Based upon the adjustment to the orifice size needed, the controller 22 may adjust the input command to the hydraulic valve 34. In other words, the controller 22 may determine the necessary current output to the actuator 46 at the retrieved pump flow to achieve the commanded velocity for the given input command of step 60.

For example, if for a given input command, the pump flow decreases, thereby decreasing fluid flow through the hydraulic valve 34, the controller 22 may (upon referring to the pre-set look-up tables or databases) increase the size of one or more of the orifices 48-52 (by way of adjusting the input command) to increase the flow of fluid through those orifices for maintaining the fluid flow for the input command. Relatedly, if for the same input command, the pump flow increases, thereby increasing the flow of fluid through one or more of the orifices 48-52 (by adjusting the input command), the controller 22 may reduce the opening area of one or more of those orifices to maintain the flow of fluid for that input command. Upon determining the amount of adjustment (e.g., adjustment to the opening area of the orifices 48-52 and therefore the adjustment to the input command), the controller 22 may generate a current command for actuating the actuator 46 of the hydraulic valve 34 to vary the orifice size. The current command may be transmitted to the actuator 46 via the communication link 36 at a step 66. The process then ends at a step 68.

The above process of adjusting the opening area of the orifices 48-52 of the hydraulic valve 34 for a particular input command and a given pump flow is performed each time an input command is received by the controller 22 for actuating the hydraulically powered device 42.

Turning now to FIG. 4, an exemplary graphical representation 70 illustrating a relationship between the input controller 26 and a valve command is shown, in accordance with at least some embodiments of the present disclosure. As shown, the X-axis of the graph 70 is the percentage of the total movement of the input controller 26 (e.g., the input controller may be moved twenty percent of the way, representing how much a joystick, for example, may have moved) and the Y-axis represents the valve command in percentage or, in other words, the percentage of the total available opening area of the orifices 48-52. The graph 70 shows three plots including, a first plot 72, also known as the benchmark plot, a second plot 74 and a third plot 76.

The benchmark plot 72 identifies the relationship between an input command issued by the input controller 26 and the valve command or the orifice size for a certain pump flow. The purpose of the controller 22 is to ensure that for variations in pump flow, the fluid flow achieved by the valve command for the corresponding input command in the benchmark plot 72 remains the same. The second plot 74 identifies the adjustment to the valve command needed when the pump flow corresponds to a pump flow that is about thirty liters per minute (30 L/min) below the pump flow at the benchmark plot 72. Specifically, the second plot 74 shows that as the pump flow decreases, the opening area of one or more of the orifices 48-52 of the hydraulic valve may need to be increased to allow for more hydraulic fluid to flow through, thereby accounting for the decrease in the pump flow and maintaining the flow of fluid at the benchmark level for that valve command. Similarly, the third plot 76 identifies the adjustment needed to the valve command when the pump flow increases beyond the benchmark level. Thus, when the pump flow increases, for example, by about thirty liters per minute (30 L/min) above the benchmark level, the opening area of one or more of the orifices 48-52 may be reduced to reduce the flow of hydraulic fluid, thereby accounting for the increase in the pump flow and maintaining the valve flow at the benchmark level.

It will be understood that the graph 70 is exemplary. While the graph 70 shows the plots for two exemplary pump flows, a similar plot for various other pump flows may be provided and pre-set within the controller 22. Furthermore, while the graph 70 has been shown with respect to pump flow, other parameters, such as engine speed, that affect pump flow may be utilized instead as well. Again, it will be understood that the pump flow may be determined, sensed and/or measured in several different ways, such as, via engine speed and sensed flow through the pump 38. Other ways to determine, sense and/or measure pump flow are also contemplated and considered within the scope of the present disclosure.

By virtue of controlling the flow of fluid through the hydraulic valve 34 and making the flow independent of the pump flow, the present disclosure provides a mechanism to not only improve the performance of various hydraulically powered devices, but also achieve a faster response from those devices. Without having to worry about the variations in pump flow on the fluid flow, the efficiency and productivity of the operator is increased as well and the operator may have a better control on the vehicle and the various hydraulically powered implements.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims. 

What is claimed is:
 1. A method of controlling fluid flow in a work machine, the method comprising: receiving an input command by a controller configured to control a fluid flow, the input command generated by an input controller; receiving a parameter indicative of pump flow by the controller; determining a first valve command corresponding to the input command; and determining a second valve command based upon the parameter that achieves the fluid flow to an actuator corresponding to the first valve command.
 2. The method of claim 1, wherein the first valve command and the second valve command are percentages of total available opening area of at least one orifice of at least one hydraulic valve.
 3. The method of claim 2, wherein determining a second valve command comprises increasing the percentage of total available opening area of the at least one orifice when a pump flow falls below a benchmark pump flow, the benchmark pump flow corresponding to the first valve command.
 4. The method of claim 2, wherein determining a second valve command comprises decreasing the percentage of total available opening area of the at least one orifice when a pump flow rises above a benchmark pump flow, the benchmark pump flow corresponding to the first valve command.
 5. The method of claim 1, wherein the first valve command is determined by referring to a look-up table.
 6. The method of claim 1, wherein the second valve command is determined by referring to a look-up table.
 7. The method of claim 1, wherein the parameter is determined by engine speed.
 8. The method of claim 1, wherein based upon the second valve command, the controller generates an output signal that is transmitted to the at least one hydraulic valve.
 9. The method of claim 8, wherein in response to the output signal, the fluid flow through at least one hydraulic valve is varied.
 10. A system for controlling fluid flow through a hydraulic valve in a work machine, the system comprising: an input controller to generate an input command; a parameter determinator to determine pump flow of the work machine; and a controller configured to receive the input command and the pump flow, the controller further configured to determine a first valve command corresponding to the input command and a second valve command based upon the pump flow that achieves the fluid flow to an actuator corresponding to the first valve command.
 11. The system of claim 10, further comprising at least one hydraulic valve at least indirectly connected to the controller, the at least one hydraulic valve configured to receive the first and second valve commands to control the fluid flow therethrough.
 12. The system of claim 11, wherein the at least one hydraulic valve is a non-compensated valve.
 13. The system of claim 10, further comprising a pump at least indirectly connected to an engine of the work machine, the pump also at least indirectly connected to at least one hydraulic valve.
 14. The system of claim 13, wherein the pump flow is determined by engine speed.
 15. The system of claim 10, wherein the second valve command is greater than the first valve command when the pump flow is below a benchmark pump flow corresponding to the first valve command.
 16. The system of claim 10, wherein the second valve command is lesser than the first valve command when the pump flow is above a benchmark pump flow corresponding to the first valve command.
 17. A work machine, comprising: an engine; an input controller for generating a plurality of input commands; a pump flow sensor for determining a pump flow; and a controller in at least indirect communication with the input controller and the pump flow sensor, the controller configured to determine a first valve command corresponding to the plurality of input commands, the controller also configured to determine a second valve command that achieves a fluid flow to an actuator corresponding to the first valve command when variations in the pump flow occur, the first and the second valve commands used to control the fluid flow to the actuator through a hydraulic valve.
 18. The work machine of claim 17, wherein the work machine is a small track type tractor.
 19. The work machine of claim 17, wherein the fluid flow through the hydraulic valve to the actuator is independent of the pump flow.
 20. The work machine of claim 19, wherein by making the fluid flow to the actuator independent of the pump flow, performance of an implement controlled by the hydraulic valve is improved. 